1. Field of the Invention
The present invention relates generally to height control systems for controlling the height of a construction machine, and more particularly, but not by way of limitation, to such systems for use in slipform paving machines.
2. Description of the Prior Art
In all construction machines which are utilized for preparing a ground surface, such as road milling machines, surface stabilizing machines, ground trimmer machines, or in construction machines for forming structures on a ground surface, such as a slipform paving machine, one important factor is the control of the height of the working implements and thus the grade or height of the ground surface being prepared or the structure being formed.
Such construction machines typically take a reference reading from a string line which has been placed on one or both sides of the intended path of the machine, or in some instances a reference is taken from an existing structure such as a previously graded surface or the like.
When the construction machine takes its height reference from a single string line that has been placed along one side of the path which the construction machine is to follow, the side of the machine adjacent the string line, which may be referred to as a reference side of the machine, has its height controlled with reference to the string line. Then, in order to orient the machine in a desired orientation relative to the ground surface, the opposite side of the machine, which may be referred to as a control side, may be controlled in response to a cross-slope sensor placed on the machine frame. If it is desired that the prepared surface or the formed structure be exactly horizontal, then the cross-slope will be controlled to be zero so that the entire prepared surface or formed structure is horizontal and at the desired elevation with reference to the reference string line.
If it is desired that the prepared surface or formed structure have a cross-slope, for example if a road surface is to be sloped from one side of the road toward the other side of the road, then the control side height may differ from the reference side height, all of which can be determined via the cross-slope sensor placed on the frame.
While controls of the type just described may be perfectly suitable for equipment with very rigid frames such as for example a typical road milling machine, an additional problem is encountered with very wide equipment, such as for example a grade trimming machine or a slipform paving machine. Such equipment may be designed to prepare or pave surfaces having widths as much as 24 feet or even greater. Furthermore, such construction equipment is often constructed such that the machine frame can be varied in width so as to accommodate paving of different widths. Such frames may also be variable in length to accommodate the installation of additional ground working equipment, such as for example the placement of a dowel bar inserter behind a slipform paving machine.
With these relatively wide frames, and particularly with frames which are extendable in width and/or length, a problem may be encountered with the distortion of the machine frame due to its inherent flexibility and the very heavy loads placed on the frame.
Accordingly, improved height control systems for construction equipment frames are needed to address this problem of frame distortion.